Many semiconductor-type process tools have a transfer passage, such as a loadlock, which limits the size and shape of substrates and substrate holders that can be inserted into the tool's process chamber. Many of these semiconductor-type process tools are optimized for processing of substantially circular substrates, such as 300 mm silicon wafers. However, there is a demand to use these process tools for substrates other than those that the tools were originally designed to process. For example, there is a demand to use these tools to process non-circular substrates. There is also a demand to process smaller diameter substantially circular substrates. Consequently, there is a need for substrate holders which can accommodate these differently sized and shaped substrates for processing in the aforementioned tools.
Devices such as multiple quantum well (MQW) light emitting diodes (LEDs) are fabricated on small substrates—typical 2, 3 or 4 inches in diameter. These devices may be gallium nitride (GaN) based. GaN based materials have historically been fabricated using metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) processes. Recently, however, hydride/halide vapor phase epitaxy (HVPE) has been demonstrated as a viable alternative process. HVPE offers the possibility of high volume manufacturing (HVM) at low cost. However, to provide cost effective HVM solutions for fabricating such devices, there is a need to process the device substrates in batches on production-worthy processing tools. Consequently, there is a need for substrate holders optimized for carrying multiple small substrates. Furthermore, there is a need for such substrate holders to be compatible with the production-worthy processing tools and to be optimized for high throughput at high yield.